Ground water and raw water, which are used for tap water production often contain high amounts of iron and manganese with regard to health, and these amounts have to be reduced before the water, from health and taste reasons, can be used as tap water. EP-A-0 160 774 describes the use of a zone for oxidation and precipitation of iron and manganese where water containing oxygen or oxygen producing compounds intermittent are added to the zone via satellite wells arranged around extraction wells. Hereby water is fed only to a few satellite wells and simultaneously water is extracted from adjacent situated satellite wells. Oxygen added creates a suitable growth environment for microorganisms present in the ground, which microorganisms together with chemical and/or biochemical processes provides for a precipitation of iron and manganese in the zone/ground layer, which will serve as a filter as well.
EP-A-0 154 105 describes reduction of nitrate in ground water by means of denitrification in a reduction zone created between injection wells also arranged around one or more extraction wells.
It is previously known to create reaction zones in aquifers to obtain an oxidation and a precipitation zone or a reduction zone between a number of injection wells arranged around one or more extraction wells in such reaction zones, whereby the zone desired is created intermittently or continuously between each pair of adjacently situated injection wells by introducing oxygen, oxygen containing gas or oxygen releasing compounds in the water of the two wells when one creates an oxidation and precipitation zone, or introduce an oxygen consuming compound in the two wells to obtain a reduction zone, and whereby one pumps the water of one of the wells from below and up, and from the top and downward in the other well so that a circulation circuit is created in the aquifer between the two wells.
Thereby the injection wells consist of an outer tube being perforated and water permeable at least in the ground water containing part of the tube. In SE-C-466 851 there is a solution where an injection well tube contains a sealing around an intermediate tube part introduced into the outer tube, and where one by arranging different air supply tubes obtains a desired flow direction in the respective injection wells to obtain a top-downward, and below-upward flow, respectively. By operating with air as a transport directing means it is, however, difficult to reach a reduction in the aquifer without adding an excess of reducing agent as the air contains about 21% of oxygen.
In another embodiment of this idea one has a first tube outgoing from a circulation vessel arranged in the upper part of the injection well tube, which first tube ends in the upper part of the aquifer, and which well tube at its mouth is provided with a first pressure inlet means to form an upper injector, and a second tube being tightly sealed off from the upper part by means of a balloon shaped body, whereby the second tube receives a second pressure inlet means arranged above the sealing means to form a second injector so that when the first pressure inlet means is being activated water will become sucked into the upper part of the injection well tube and be pressed upwardly in the first tube, and downward into the second tube to be pressed out into the aquifer while when the second pressure inlet means is being activated water is sucked in from the lower part of the injection well tube and is pressed upward in the second tube and out through the first tube and from there, out into the aquifer.
The problem of these embodiments is that no correct control of the flows between different injection wells is not obtained as the hydraulic situation from one well is divided into two layers using a sealing which means partly a precipitation problem, partly a bad circulation.